Conditional-lethal temperature-sensitive (ts) and other point mutants of human adenovirus 2 will be constructed in vitro by mutagenizing specific segments of the viral DNA. The early gene blocks and the inverted terminal repetitious regions located at both the molecular ends will be mutagenized with single strand-specific mutagen, NaHSO3 after limited digestion with exonuclease III. In addition, ts mutants in the gene blocks located at the molecular ends as well as in the internal segments will be constructed by mutagenizing specific restriction fragments of the viral DNA and joining with the rest of the genome by specific marker transfer. Ts mutants defective in early and late viral genes will be characterized with regard to induction of cellular transformation of non-permissive rat cells, viral DNA synthesis, regulation of expression of viral genes, synthesis of viral polypeptides, and altered nucleotide sequences at the inverted terminal repetitious regions.